1. Field of the Invention
The present invention generally relates to improvements for guardrail terminal installations and, in particular aspects, the invention relates to improved support posts and support systems for guardrail terminal systems that have safety end treatments.
2. Description of the Related Art
An important aspect of guardrail design is the ability of the guardrail to resist rupture and prevent penetration of the rail by a vehicle that impacts the guardrail end. For that reason, conventional guardrail installations are provided along their lengths with “strong” support posts that provide very little give when impacted by a vehicle. “Strong” support posts include 7″ diameter wood posts, W6×9 steel section posts and 6″ by 8″ wood posts.
Recently, it has also become important that a guardrail installation not present a hazard to a vehicle during an “end-on” impact where the guardrail installation is impacted from its end by a vehicle. As a result, a number of solutions have been proposed and used for eliminating the upraised end of the guardrail for making it safer.
The guardrail extruder terminal (GET) and slotted rail terminal (SRT) are known safety end treatments for a guardrail assembly that permit the guardrail assembly to safely absorb some or all of the vehicle's kinetic energy during an end-on collision, thereby eliminating the hazard associated with the upraised end. These end treatments are desirable because they absorb the energy of an end-on collision in a controlled manner to help bring an impacting vehicle to a safe stop or they allow the vehicle to safely “gate” through the terminal after absorbing some of the vehicle's energy. The GET is described in U.S. Pat. Nos. 5,078,366 and 4,928,928. The SRT is described in U.S. Pat. Nos. 5,547,309 and 5,407,298. Those patents are incorporated herein by reference. These end treatments were originally designed so that the support posts of the terminal would be readily frangible, “breakaway” posts made of wood. Holes were usually drilled through the post near the ground line in order to weaken the post at that point. Guardrail support posts downstream from the terminal are typically solid wooden posts used to securely anchor the midportion of the guardrail assembly to the ground. As the guardrail collapsed or became flattened by the end treatment, the breakaway posts would be broken at or around the ground line.
There are, however, drawbacks to using strong posts along the length of the end-treatment terminal. The strong posts must be weakened in some manner to accommodate end on impacts to the terminal. These modifications are costly and time consuming and, if done improperly or forgotten, can result in a significant safety hazard for motorists.
The inventors believe that, to date, guardrail terminals have used entirely strong support posts that have been modified by drilling holes or using other means to cause the post to breakaway. An improved guardrail installation would be desirable.